I'm going to give you a tip. Put cardboard under your truck completely (you only see cardboard no ground). Get in pump the brakes, pump the heck out of them. See if you have a leak. I had a pin hole leak (literally less then .5mm) that also caused my brake issue. Never had air in the system but it was enough to have it lose pressure.

 

Thanks for the input on using cardboard. I will give that a try.

 

No problem! This is definitely an odd issue.